Water-laid webs comprising water-fibrillated, wet-spun filaments of an acrylonitrile polymer and method of producing them



06L 1957 w. M. WOODING ETAL 2,81

WATER-LAID WEBS COMPRISING WATER-FIBRILLATED, WETSPUN FILAMENTS OF AN ACRYLONITRILE POLYMER AND METHOD-0F PRODUCING THEM Filed Sept. '17. 1953 Ufllfc sggtgs patgnt WATER-LAID WEBS COMPRISING WATER-FIBRE..- LATED, WET-SPUN FILAMENTS OF AN ACRY- LONITRILE POLYMER AND METHOD OF PRO- DUCING THEM The present invention relates to. water-laid webs contain'ingfibrillated wet spun polynitrile filaments, and processes for. the manufacture thereof. The invention includes paper, paperboard and pulp-preforms composed of fibrillated wet-spun polynitrile filaments and mixtures of said filaments with cellulosic fibers.

The manufacture of synthetic organic filaments has long constituted an important part of the chemical industry, such filaments beingsubstantiallywholly employed for the manufacture of textiles. The filaments are produced by extrusion, and hence the filaments, when viewed under a microscope, .havethe appearance of smooth, glassy rods.

Accordi-ngto one methodfor the manufacture of these filaments, the hotmelt"method,ra thermoplastic organic polymer is melted and is extruded through spinnerettes into cooler air. A filamentforms when the polymer has cooled below its meltingpoint.

According to a. secondor air dry method, a polymer is dissolvedin a volatile solvent and the solution is extruded througlispinnerettes. into air. A filament develops upon volatilizationof the solvent.

According to a third or wet spinning method, the polymer isdissolved ina suitable solvent, and'the solution is extruded through spinnerettes into a liquid in which the solvent dissolves but in which the polymer is insoluble. A filament develops when the solvent is leached from the polymer by the body of liquid into which the dissolved polymer is extruded. The filament thus obtained is termed wet spun filament to distinguish it from filament which has been produced by the other methods mentioned.

The present invention relates to filaments produced by the wet-spinning process, and particularly to wet-spun polynitrile filaments. The term polynitrile filaments is used in its ordinary sense'to designate a filament formed of linear hydrocarbon chains having nitrile groups attached thereto. Such linear hydrocarbon chains are formed by polymerization of one or more o e-unsaturated nitriles aloneor, if desired, in admixture with a small amount of a modifying material copolymerizable therewith.

The discovery has now been made that paper and other felted webs formed from wet-spun, heat-bonded, fibrillated polynitrile filaments alone or in admixture with papermaking cellulosic fibers, possesses many beneficial properties of which the most important are these.

(1) Paper composed wholly of polynitrile filaments remains substantially completely dimensionally stable when exposed to atomspheres ofvarying relative humidities and even When contacted with water. Surprisingly, this remains true even though up to about 50%-80% by weight of cellulosic fibers are incorporated therein. Very surprisingly, the presence of 20% by weight of polynitrile filament in cellulosic paper reduces elongation by about 50%. Paper wholly composed of cellulose fibers, however, usually elongates noticeably on contact with water.

(2) Paper wholly composed of polynitrile filaments retains an appreciable portion of its normal dry. tensile strength when wet, and tensile strength values as high as of corresponding dry strength have been obtained. A paper of useful wet strength is obtained even when up to about 50% of the fibers are replaced by cellulose fibers. Paper wholly composed of cellulose fibers, however, loses practically all of its tensile strength when immersed. in water.

(3) Paper composed wholly of these polynitrilefilaments possesses good dry tensile strength. Values up to 3-4 lb./in. are commonly attained at a basis weightof 50 lb. (25 x 4-0/500) and paper of much higher strength has been produced. Thisstrength is improved by the presence of a small amount of. papermaking cellulose fibers.

(4) Paper wholly composed of polynitrile fibers dis-. plays far higher resistance to penetration by water and by ink than corresponding cellulose paper containing the same amount of. rosin size. This effect, surprisingly, persists in large part even though up to about 50% of the polynitrile fibers. are replaced by cellulose fibers.

(5) Paper wholly composed of polynitrile fibers is muchmore resistant than the best cellulose paper to tendering, degradation and discoloration under prolonged exposure to ultraviolet light and oxygen. It is therefore a paper of excellent permanence.

The products of the present invention may be employed for any purpose for which similar cellulosic products have previously been employed in the past. Because of their combination of good wet strength, chemical resistance, almost perfect dimensionalstability under humid conditions and wetting by water, and great resistance to oxygen and ultraviolet light they are particularly useful as paper used in recording instruments, punch cards for calculating machines, ledger andother permanent record paper, map paper, graph paper, and blueprint paper.

It has further been discovered that wet-spun polynitrile filaments, when refined in aqueous suspension in ordinary papermaking equipment, fibrillate to confer an excellent latent bonding property thereon, and that this latent prop.- erty is developed when the thus water-fibrillated filaments are sheeted and dried at 250"F. On drying in this manner the filaments strongly bond with themselvesand presumably with any cellulosic fibers which may be present to form a felted web of very useful dry strength. The bond thus developed is autogenous, that is, it results from the combination of steps referred to and is not due to the effect of any added strengthening agent, although a strengthening agent may be added if desired to increase the strength still further.

From the foregoing it will be seen that the webs of the present invention have as their essential component Water-laid, felted, heat-bonded, water-fibrillated wet-spun polynitrile filaments. In other words, in the webs the filaments are interlaced or felted resulting from the step of sheeting or water-laying the filaments from aqueous dispersion on a wire screen and the fibrillations of the filaments are heat-bonded resulting in a web of substantial dry strength.

The process for the manufacture of paper according to the present invention comprises three principal steps.

in the first step, wet-spun polynitrile filamentsoficonvenient length and denier are refined in aqueous suspen-. sion until the filaments have fibrillated. In this stepthe filaments acquire felting properties and also acquire latent heat-bonding properties.

In the second step, the fibrillated filaments, alone or in admixture with other felting fibers, are sheeted-to form a water-laid web.

By fibrillatedfilaments in. the specification and the claims which'follow, we meanfilaments bearing sliver.- like fibrils distributed along their length.

In the third step, the web is heated to dry the same and to develop the latent bonding properties imparted to the polynitrile filaments by the refining step. The refiningis preferably performed in the same manner in which ordinary cellulosefibersjare refined to develop their papermaking properties, and includes A the ordinary process of beating; The time required,in the case of polynitrile filaments, however, is usuallysomewhat longer thanin the case of cellulose fibers, I

Any equipment capable of refining cellulose fibers may be used including beaters of the Niagara and Hollander types, Hydropulpers, Dynapulpers, jordans, and Mordens.

The filaments are refined at any convenientconsistency,

normally 1%-2%, and no heating of the stock is neces-' sary.

The duration of the refining for the production of paper of optimum strength is not subject to a simple rule stated in terms of time or.in terms of the freeness of the refined suspension. The time required for the refining is a function of such independent variables as the speed of the beater, pressure on the bedplate arm, number and width of the beater bars, and diameter and fibrillating character of the polynitrile fibers. The freeness of polynitrile pulps at any given degree of fibrillation varies appreciably with the denier and length of the filaments employed as well as with the precise character of the fibrillation developed by the refining equipment employed. As a result, the minimum effective amount of fibrillation can best be determined by a simple laboratory trial, the least amount of fibrillation necessary to develop a filament of commercially useful felting and heat-bonding properties with development of a somewhat more than selfsustaining sheet being that required to form a laboratory handsheet which, when dried at 240 F. has at 50 lb. basis weight (25" x 40"/500) a dry tensile strength of about 2 lb./ in. Preferably, the beating will be continued until a sheet formed in the same manner has a dry tensile strength of 6 lb./in. or better, this value being in the range of maximum economically developable dry strength.

The refining may be extended resulting in the development of filaments of stronger felting properties. The optimum duration of the refining likewise is most accurately determined by laboratory trial, samples being withdrawn and made into paper as the beating progresses as illustrated in Example 1.

The optimum degree of beating for formation of paper of best dry and wet tensile strength may very conveniently be estimated by observing the filaments under a lowpower microscope from time to time as the beating progresses and discontinuing the beating when the filaments have attained a degree of fibrillationfound 'by experience to be about the optimum. Means for making this comparison are afforded by the drawing, in which:

Figure 1 is a photomicrograph of 3-denier wet-spun polynitrile filaments of textile making grade in the form in which they are manufactured;

Figure 2 is a photomicrograph of the same filaments fibrillated by beating in a laboratory Valley beater to an extent suflicient to yield paper of substantially maximum dry strength; and

Figure 3 is a photomicrograph of the filaments of Figure 2 which have been further beaten, resulting in moreextensive fibrillation and development of paper of substantially the same dry strength.

The photomicrographs were made at a magnification of 100 X.

From Figure 1 it will be seen that in their unbeaten form the filaments possess no capacity to form a waterlaid, felted sheet. The form of fibers shown in the figure is typical of all organic synthetic filaments currently produced.

From inspection of Figure 2 it will be seen that beating was substantially complete when the filaments developed numerous short ramified, sliver-like fibrillations which were well-distributed along their length. The filaments,

. a r 4 although flattened, substantially retained their original smooth structure and developed only a minor amount of striation and splitting.

Figure 3 shows the surprising extent to which polynitrile filaments can be fibrillated while producing paper of very satisfactory strength. In this figure the filaments 'show a substantial amount of striation and splitting, and have a mossy appearance.

From the figures it is evident that for best results the filaments will be refined or beaten until they have fibrillated approximately to the extent shown in Figure 2.

In the second step of the general process, the waterfibrillated filaments thus produced are sheeted to form a web. The sheeting is performed as if the fibers were cellulose fibers, without need for altering standard procedures. The web may have any desirable caliper so as to result in the formation of a tissue, a paper, a paper board or a building board as is known in the art, and the web may be subjected to suction to facilitate drying and may be passed through dandy rolls, calender rolls, and super calender rolls in the same manner as webs wholly composed of cellulose fibers.

In the third step the web is heated until dry and it is important that the drying take place at a sutficiently elevated temperature to cause the fibrillated filaments to bond either to themselves or to such cellulose fibers as may be present. Negligible bonding takes place when the filaments are dried at room temperature, and the bonding is developed as the drying temperature is increased.

As a practical matter, to secure a useful bonding effect the minimum drying temperature should be about F., the heat saved by use of a lower temperature being more than offset by the weakness of the resulting web. At the other extreme, the temperature of the drying rolls need not exceed 250 F. as at that temperature the web dries very rapidly and a paper of excellent dry strength It is evident, therefore, that the drying and' is obtained. the heat bonding may be performed in the same equipment as ordinary cellulosic paper is customarily produced commercially.

The heat-bonding referred to does not melt the filaments or the fibrils as examination by microscope of paper manufactured in accordance with the present invention shows that the fibrillated polynitrile filaments in the paper have the same general appearance as those of Figures 2 and 3. The evidence, therefore indicates that the effect of heat-bonding is only a surface coalescence of the interfelted fibrils.

The heating may be continued after the web has become dry but unless required by a particular constituent of the web, this further heating is without advantage although doing no harm.

The general process described may be extensively modified. For example, cellulose fibers, including groundwood, may be introduced into the suspension before the suspension is sheeted. Preferably, the cellulose fibers are beaten separately from the polynitrile fibers, but in some instances they may be beaten in admixture therewith, due regard being had to the fact that cellulose fibers hydrate and fibrillate more readily than the polynitrile filaments fibrillate when both are refined in the same manner.

In addition the suspension may contain before sheeting minor amounts of any of the other fibers employed in the manufacture of paper including glass fibers, absestos fibers, silk fibers, and non-fibrillated synthetic filaments.

The fibrillated polynitrile filaments of the present invention are compatible with cellulose fibers in all proportions and paper of improved dimensional stability is obtained when only a very minor proportion of polynitrile fibers are present. There therefore does not appear to be any amount of polynitrile filaments too small to have a beneficial effect on the dimensional stability of cellulosic webs.

\ The beneficial effect of the presenceof the polynitrile 5 filaments in such paper becomes very significant when as little as 5% of these filaments are present, paper formed from such a. mixture exhibiting about a 20%"25% improvement in dimensionalstability.

In the case of'sized 'pap'er the'pre'sence'ofmore than about 30% by weight of the: polynitrile fiber-causes the sheet to exhibit substantially greater resistanceto penetration by ink and water than would otherwise be the case:

When paper contains about 50%80% of the polynitrile fibers the paper develops substantially complete immunity from dimensional change in-z-thepresence of water or humid atmospheres and, when sized with as little as 2% rosin size, exhibits a resistance to penetration by ink and by water substantially equal to that called for by the most stringent requirements of the trade.

Increasing the amount of 1 fibrillated polynitrile filaments in the paper usually increases the'beneficial prper ties referred to.

The fibers may carry any of the widely used cationic cellulose-substantive amine-aldehyde wet strength resins. Among such resins are the melamine-aldehyde condensates of U. S. Patents Nos. 2,345,543and 2,559,220, the melamine-monoureide-formaldehyde resins of U. S. Patent No. 2,312,688, the urea-formaldehyde-sulfoxylate resins of U. S. Patent No. 2,556,898, and the polyarylbignanideurea resins of U. S. Patent N01 2,596,014; In addition there may be used the urea-(aminoalkyl) formaldehyde resins of Schiller et al. co-pending application No. 262,168; filed on December 17, 1951, now" U. S. Patent No. 2,698,787. These resins are substantively adsorbed both by cellulose fibers and by the polynitrile fibers, and-are, therefore, advantageously added to the suspension before it is sheeted in amounts sufficient to cause from to 5% thereof to be adsorbed on the fibers. In addition to increasing the dry and wet strength of the Webs for-med, the resins markedly increase their abrasion resistance.

The fibrillated polynitrile filaments of the present invention are very receptive to the sizes commonly employed in the manufacture of paper, and may be sized in the respective manners in which these sizing agents are applied to cellulose fibers.

Thus the polynitrile fibers may be sized by the beater addition method wherein a sizing material such asanionic or soap sizes including sodium stearate, rosin" size and fortified rosin size, emulsified Wax sizes, and emulsified asphalt sizes are deposited by the addition of alum or by the action of a cationic surface active agent. Moreover, the fibers may be sized by the direct addition of cationic sizes which are substantively adsorbed by the fibers.

Moreover the webs may be sized by existing tub sizing methods in the same manner as cellulosic webs.

The particular manner in which the sizing is applied and the amount thereof deposited plays no part in the present invention.

The Wet-spun polynitrile filaments consist essentially of linear carbon chains carrying nitrile groups.- In general, any a,B-unsaturated nitrile may be used. Because of its-ready availability and excellent results obtained, acrylonitrile is preferred, and the filaments may be obtained by polymerizing this material alone or in admixtur with a small amount, up to about by weight, of a suitable modifying agent copolymerizable therewith such as an mil-unsaturated amide or ester. The polymerization is preferably performed in aqueous emulsion in the presence of ammonium'persulfate as catalyst. The polymer or copolyrner is then dissolved in a suitable solvent such as aqueous sodium thiocyanate and the resulting gel is extruded into water.

Detailed methods for the preparation of these fibers are set forth in numerous U. S. Patents, including Nos. 2,558,735, 2,595,847, 2,613,195, 2,611,929 and 2,644,803 respectively granted to Cresswell, Hoxie, Craig, Ham, and Cresswell. Such patents are incorporated by reference into the present specification. These patents show that the fibers may be prepared from polymerized acrylonitrile or a copolymerized mixture of acrylonitrile and up to about 15 by weight" ofat least one monomer copolymerizable therewith.

The polynitrile fioers may-contain minor amounts of such materials such-as" are normally presentin textile fibers, for example, delusterants, antistatic agents, and dyes. Thewebs obtainedmay contain, in addition to the polynitrile and cellulose fibers referred to, small amounts of other felt-forming fibers or anyof the softening agents, sizes, impregnating agents," coating materials and resins commonly employedin the manufacture of paper.

The invention will 'be more particularly described with reference'to th'e'ex'amples which follow. The examples do not 'limit the scope of'the invention but are for purposes of-illustration only.

Example 1 Wet-spun, 3-deni'er polyacrylonitrile textile filaments were hand chopped toabout A"1" length, slurried with water to a consistency of 1% and beaten in a 1lb. Valley laboratorybeater with, 10 lb. on the bedplate arm.

Samples of the suspension were withdrawn during the beatingrasindicated in the table below, and were formed intopaper on a Nash handsheet machine. One set of sheets was dried at room: temperature and a second set of sheets was dried on a drum drier at 240 F. for one minute. v

The' air-dried sheets possessed practicaliy zero dry strength and were therefore discarded.

The drum-dried sheetswere conditioned at 73 F. and 50% relative-humidity for 24 hours and then weretested to-determinetheinwetand drytensile strength. The tear strength of one sample was alsodetermined. Resultsare as follows:

. Tensile, Strength;

- Hours Lb./in. Wet Tear, lb. Sample No. Beaten Strength, (Elrnen- Percent dort) Dry. Wet

l Web too weak to be removed from wire. 1% 23 t 3. 55 57 b 1%- 6. 27 4. 30 2 6. 23" 4. 93 79 2%- 6.1 5.00 1

e As percent of dry strength.

b Thesefilaments correspond to the fibers of Fig. 2.

B Thesefilaments correspond to the fibersof-Fig. 3.

This table indicates that paper. ofvery satisfactory Wet and dry strength'can be prepared from Wet-spun polynitrile filaments beaten to about the extent shown in Figure 2, and that the filaments can be extensively beaten thereafter with no substantialdiminution of dry strength and with some benefit to its-wet strength. The tear value obtained placesthe paper well within the useful range.

The following textile filamentswere chopped to A"1 length andbeaten for 2 /4 hours in the same manner as the wet-spun polynitrile filaments: ethylene terephthalate filament; nylon filament; cellulose acetate filament; regenerated-cellulose filament; vinyl'chloride-vinyl acetate copolymer filament; and polyacrylonitrile filament formed by the hot melt process. In each instance the sheets formed were so weak that they could not be removed from the wire without breaking or tearing. Examination of the beaten filaments by microscope showed that no significant fibrillation-took place, the filaments being broken and flattened but otherwise having the general appearance of the filaments of Figure 1.

Example 2 Chopped, wet-spun polyacrylonitrile filaments corresponding to the filaments of- Example 1 were beaten for 1% hours according to Example 1. The resulting suspension of fibrillated filaments having the appearance of the filaments of Figure 2 was divided into three aliquots.

One aliquot was reserved as control.

To the second aliquot was added.3% of Parez resin No. 607 solution (a melamine-formaldehyde acid colloid produced by the process of Wohnsiedler et al. U. S. Patent No. 2,345,543.).

To the third aliquot was added 2% of gum rosin size and then 2% of alum.

The percentages stated represent the dry weight of the materials added based on the dry weight of the fibers.

The aliquots were then sheeted according to Example 1. The handsheets obtained were conditioned at 73 F. and a relative humidity of 50% for 24 hours, and tested with the following results. Results are included on paper made in the same way from bleached northern kraft pulp beaten to a green freeness of 460 cc.

1 Based on dry weight of the sheet. 9 By B. K. Y. test. 3 By Currier test (slack scale).

The data show that a significant improvement in ink and water resistance is effected when the paper contains about 30% of polynitrile fibers, the improvement rising POLYA ORYLONITRILE PULP Tensile 2 Burst 3 Ex. Treatment Basis Abra- Ink H H10 Wt. sion 4 Resist. Resist. Swell 7 Dry Wet Dry Wetv BLEACHED NORTHERN KRAFT PULP 1 Control 43. 3 25. 4 0.6 43. 5 5.0 215 0 0 0.75 2 Perez 607.--- 44. 7 32.8 8. 4 57.0 24. 5 687 0.60 3 Rosin Size--- 43.6 23 2 1.8 32.0 5. 5 62 675 32 0.68

1 Lb. per x "{500 ream.

2 Lb./i.n., by Schopper test.

3 Lb./i.n. by Mullen test.

4 Cycles, by Taber test.

5 Seconds, by B. K. Y. test.

0 Seconds, by Currier test (slack scale).

7 Percent elongation of 20 cm. strip after 24-hr. immersion at 70 F.

These results show the following: 7 I v (1) Paper made from untreated fibrillated wet-spun polyacrylonitrile filaments intrinsically possesses'f far greater wet tensile and wet bursting strengththan untreated paper made from normal cellulose fibersfl j (2) Polynitrile paper is substantially completely dimensionally stable in the presence of water, whereas cellulosic paper swells extensively under the same conditions. The presence of neither sizing material nor wet strength resin had any appreciable eifect'upon the dimensional stability of the polynitrile paper.

(3) Fibrillated polyacrylonitrile filaments are receptive to both rosin size and to cationic, colloidal aminealdehyde, wet strength resins, so receptive in fact that rosin size causes the filaments to become far more resistant to penetration by ink and water than cellulose fibers.

Example 3 The effect of the presence of fibrillated polynitrile filaments upon the ink and waterresistance of rosin-sized cellulose paper containing increasing amounts of fibrillated polynitrile filaments is illustrated by the following.

To aliquots of bleached northern kraft pulp beaten to a green freeness of 460 cc. was added beaten wet-spun polyacrylonitrile filaments corresponding to the fibrillated filaments of Example. 2 to yield suspensions having the fiber composition shown in the table below. To each suspension was added 2% of rosin size and 2% of alum based on the dry weight of the fibers thereon. The suspensions were sheeted and dried in accordance with the procedure of Example 1 at a basis weight of about 46 lb. and tested by the methods of Example 2. Results are as follows, one aliquot of northern kraft pulp being processed without the addition of polynitrile filament to serve as control.

thereafter almost vertically as the content of polynitrile fibers increases.

For most purposes it is unnecessary for paper to have a water resistance (Currier test-slack scale) in excess of about 65 seconds. As a result, a 50:50 blend of cellulose fibers with fibrillated polynitrile filaments provides a paper of excellent ink and water resistance while minimizing utilization of the more costly polynitrile filaments.

Samples of the papers after conditioning for 24 hours at 50% relative humidity and 73 F. were cut into strips, 20 cm. lengths marked thereon, and the strips soaked in Water for 24 hours at 72 F. The strips were then removed, blotted to remove surface water, and measured to determine their percent of elongation. Results are as follows:

Immersion 1 Based on dry Weight of the sheet.

This table shows that there is no minimum amount of polynitrile filaments which does not improve thedimen sional stability of rosin sized cellulosic paper to some extent, that rosin sized paper containing about 20% of polynitrile filament has excellent dimensional stability, and that paper containing 50% or more of polynitrile fil ament has practically perfect dimensional stability.

The foregoing results were obtained as stated by testing handsheets formed in the laboratory. It is known Example 4 A series of unsized papers at 45 lb. basis weight (25 x 40/ 500) containing increasing amounts of fibrillated polynitrile filaments was prepared according to the method of Example 2 using the same polynitrile and cellulose fibers as were employed therein. The resulting handsheets were tested to determine their dimensional stability upon immersion in water according to Example 3. Results are as follows:

Percent Percent Fibrillated Elongation Sheet No. Polynitrlle After Filament In Immersion Sheet 1 1 Based on dry weight of sheet.

This table shows that in the manufacture of unsized paper, the presence of only 15% more of fibrillated polynitrile filament decreases elongation by about 24.5%. The presence of only 20% of the filament exerts an effect far out of proportion, this amount decreasing elongation by nearly 50%. The presence of 50% or more of the fiber decreases elongation to a negligible value.

We claim:

1. A water-laid web comprising felted, heat-bonded, water-fibrillated wet-spun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15 by weight of at least one monomer copolymerizable therewith.

2. A water-laid web consisting essentially of felted cellulose fibers and felted, heat-bonded, water-fibrillated wetspun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15% by weight of at least one monomer copolymerizable therewith.

3. A web according to claim 2 in which the fibers and filaments carry from A to 5% of their weight of a cationic amine-aldehyde wet strength resin.

4. A sized water-laid web comprising felted, sized cellulosic fibers and felted, sized, heat-bonded, water-fibrillated, wet-spun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15% by weight of at least one monomer copolymerizable therewith, the weight of said filaments being at least about 30% of the weight of the web.

5. Paper consisting of sized, felted, heat-bonded, waterfibrillated wet-spun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15% by weight of at least one monomer copolymerizable therewith.

6. Paper of improved resistance to penetration by water, consisting essentially of felted, rosin-sized cellulose fibers and felted heat-bonded, rosin-sized, water-fibrillated, wetspun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15 by'weight of at least one monomer copolymerizable therewith, the weight of said filaments being at least 30% of the weight of the paper.

7. A process of manufacturing a water-laid web which comprises refining wet-spun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15% by weight of at least one monomer copolymerizable therewith, in aqueous suspension until said filaments have fibrillated, sheeting said filaments to form a water-laid web, and heating said web at about -250 F. until dry.

8. A process of manufacturing a water-laid web which includes the steps of forming an aqueous suspension of papermaking cellulosic fibers and water-fibrillated wetspun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acryloni trile and a copolymerized mixture of acrylonitrile and up to about 15% by weight of at least one monomer copolymerizable therewith, sheeting said fibers and filaments to form a water-laid web, and heating said web at about 150250 F. until dry.

9. A process of making a sized, water-laid web which includes the steps of forming an aqueous suspension of papermaking cellulose fibers and water-fibrillated wetspun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15% by weight of at least one monomer copolymerizable therewith, sizing said fibers and filaments, sheeting the same to form a water-laid web, and heating said web at about ISO-250 F. until dry, the weight of said filaments being at least about 30% of the weight of said web.

10. In the manufacture of a cellulosic sheet wherein beaten papermaking cellulose fibers in aqueous suspension are sheeted and the sheet thus formed is dried at a temperature between 150 F. and 250 F., the improvement which consists in mixing water-fibrillated wet-spun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15 by weight of at least one monomer copolymerizable therewith, with the cellulose fibers in said suspension.

11. In the manufacture of paper from an aqueous suspension comprising water-fibrillated wet-spun filaments of paper-making length, of a polymer chosen from the group consisting of polymerized acrylonitrile and a copolymerized mixture of acrylonitrile and up to about 15 by weight of at least one monomer copoylmerizable therewith, wherein said wet-spun filaments'are fibrillated in aqueous suspension and sheeted to form a web, the improvement which consists in adsorbing on said filaments while in aqueous suspension from about A to 5% based on their dry weight, of a cationic colloidal aminealdehyde wet strength resin.

References Cited in the file of this patent UNITED STATES PATENTS 1,919,697 Grofi July 25, 1933 2,404,714 Latham July 23, 1946 2,477,000 Osborne July 26, 1949 2,535,690 Miller Dec. 26, 1950 2,558,730 Cresswell July 3, 1951 2,559,220 Maxwell July 3, 1951 2,563,897 Wilson et al Aug. 14, 1951 2,577,763 Hoxie Dec. 11, 1951 FOREIGN PATENTS 146,442 Australia May 12, 1952 674,577 Great Britain June 25, 1952 687,041 Great Britain Feb, 4, 1953 

1. A WATER-LAID WEB COMPRISING FELTED, HEAT-BONDED, WATER-FIBRILLATED WET-SPUN FILAMENTS OF PAPER-MAKING LENGTH, OF A POLYMER CHOSEN FROM THE GROUP CONSISTING OF POLYMERIZED ACRYLONITRILE AND A COPOLYMERIZED MIXTURE OF 